1. Field of the Invention
The present invention relates to a mounting structure for an oil cooler which cools engine oil or transmission oil of a vehicle.
2. Related Art
An oil cooler 101, for performing heat exchange between engine cooling water and engine oil, combined with an oil filter 102 for removing a foreign object in engine oil is illustrated in FIG. 9.
The oil cooler 101 has a core portion 101a for heat exchange. A center bolt 103 made of iron penetrates the center of the core portion 101a. By screwing a screw portion 103a formed on an end of the bolt 103 together with an engine block 104, the oil cooler 101 is fixed to the engine block 104 by a flange portion 103b of the bolt 103.
Furthermore, by screwing the oil filter 102 having a filter element 102a together with a screw portion 103c formed on the other end of the bolt 103, the oil filter 102 is combined with the oil cooler 101.
A packing 105 is provided between the oil cooler 101 and the engine block 104. A packing 106 is provided between the oil cooler 101 and the oil filter 102.
As illustrated by arrows in FIG. 9, oil discharged from an oil pump not shown flows to the core portion 101a from a passage 104a of the engine block 104, and is cooled by heat exchange with engine cooling water while passing through the core portion 101a, and flows in the filter element 102a to remove a foreign object, and reaches an oil main gallery (not shown) of the engine via a hole portion 103d formed in the center of the center bolt 103.
In short, the oil cooler 101 is fastened by the center bolt 103 with a very large force because of a reason described hereinafter. The tightening load is concentrated on a central portion of the oil cooler 101. Therefore, a ring-shaped collar 101b is provided in the core portion 101a to bear the load with the collar 101b in order to prevent a deformation of the core portion 101a caused by the tightening load.
The oil cooler 101 has been requested to be made of aluminum because of the lightening request and the like. However, if the oil cooler 101 is made of aluminum, the center bolt 103 made of iron may be loosened because of aluminum fatigue.
Since aluminum is softer than iron, fatigue is likely to occur on the collar 101b which receives the tightening load caused by screwing the center bolt 103. Furthermore, since the coefficient of linear expansion of aluminum is greater than that of iron, fatigue of the collar 101b may also be caused by hot-cold cycle, that is a temperature change caused by ON and OFF of an engine. As a result, the center bolt may be loosened, and the oil cooler 101 may be loosened in the vertical direction in FIG. 9, and the oil may leak at the packing 105 or 106.
According to the oil cooler 101 integrally assembled with the oil filter 102 by the center bolt 103, the center bolt 103 has to be tightened with larger force taking into consideration that the tightening load of the oil cooler 101 decreases as the oil filter 102 is attached and that the bolt 103 should be prevented from being loosened when the oil filter 102 is detached. Accordingly, the fatigue of the collar 101b may likely to be caused, and the bolt may likely to be loosened.